1. Field of the Invention
The present invention relates to an inkjet printing apparatus, inkjet printing method, and non-transitory computer-readable storage medium.
2. Description of the Related Art
An inkjet printing apparatus that prints information by discharging ink while scanning a print head for discharging the ink across a printing medium is known in the art. One example of such an inkjet printing apparatus is an apparatus that prints information on a front side of a printing medium, then reverses the printing medium, and prints information on a back side of the printing medium, that is, an apparatus that executes so-called double-sided printing.
It is known that an inkjet printing apparatus may suffer a phenomenon in which a printing medium is made to wrinkle due to the application of ink to the printing medium, so-called “cockling”. The occurrence of cockling increases with an increase in the amount of ink applied to the printing medium.
When cockling occurs in printing on a front side of a printing medium by the above-described inkjet printing apparatus capable of executing double-sided printing, the distance between the print head and the printing medium (hereinafter also referred to as head-to-medium distance) at the time of discharging ink to the back side changes. This may cause ink landing position deviation and lead to a decrease in image quality of a printed image. Japanese Patent Laid-Open No. 2007-152787 discloses a technique to suppress the decrease in image quality caused by cockling by calculating a drawing area for each of the front and back sides of one printing medium and, if the total of the drawing areas for each of the front and back sides is larger than a threshold, increasing the number of scans on a unit region in back-side printing.
Unfortunately, the disclosed method may have issues as detailed below.
FIGS. 1A to 1C are schematic diagrams for describing cockling when print data elements corresponding to images to be printed on a printing medium are different. FIGS. 1A to 1C illustrate cases where the image is printed by scanning a print head five times across a printing medium 3. Unit regions 81 to 85 indicate regions where the image is printed by the first to fifth scans, respectively. Each of the ratios illustrated in FIGS. 1A to 1C indicates a ratio of the number of pixel regions where pixels are formed by discharging ink to the number of pixel regions corresponding to pixels where ink can be discharged in each unit region (hereinafter also referred to as printing duty).
FIG. 1A schematically illustrates an image in which the printing duty in a divided section 83b is 100% and that in a divided section 83a and that in each of the unit regions 81, 82, 84, and 85 is 0%. The divided section 83b and the divided section 83a are included in the unit region 83, where the image is printed on the printing medium 3 by the third scan. The divided section 83b is on the downstream side in an X direction, and the divided section 83a is on the upstream side in the X direction. FIG. 1B schematically illustrates an image in which the printing duty in the divided section 83b is 20% and that in each of the other regions is 0%.
The printing duties in the regions other than the divided section 83b in each of the images illustrated in FIGS. 1A and 1B are all 0%, and no cockling occurs therein. Both images have substantially the same drawing area, which corresponds to the area of the divided section 83b. In the image illustrated in FIG. 1A, the printing duty in the divided section 83b is as high as 100%, and relatively large cockling may occur in the divided section 83b. Thus when the image illustrated in FIG. 1A is printed on the front side of the printing medium, ink landing position deviation may occur in a region of the back side that corresponds to the divided section 83b of the front side.
In the image illustrated in FIG. 1B, the printing duty in the divided section 83b is as relatively low as 20%, and cockling is not likely to occur in the divided section 83b. Accordingly, in the case where the image illustrated in FIG. 1B is printed on the front side, ink landing position deviation is not likely to occur in a region of the back side that corresponds to the divided section 83b of the front side. Even with substantially the same drawing area, when the amount of ink discharged partially to the front side is larger, cockling occurs more conspicuously and ink landing position deviation is more likely to occur in back-side printing.
FIG. 1C schematically illustrates an image in which the printing duties in divided sections 81a to 85a and 81b to 85b in the unit regions 81 to 85 in the printing medium 3 are all 10%.
In the image illustrated in FIG. 1C, the total of the printing duties for the printing medium 3 is 100% (=10%×10), which is the same as that for the printing medium 3 in the image illustrated in FIG. 1A. Because ink is discharged to all of the regions in the printing medium, the drawing area in the image illustrated in FIG. 1C is larger than that in each of the images illustrated in FIGS. 1A and 1B. However, the printing duty in each of the divided sections 81a to 85a and 81b to 85b is as low as 10%, and cockling is not likely to occur in any of the divided sections. When the image illustrated in FIG. 1C is printed on the front side, ink landing position deviation is not likely to occur in back-side printing. As is clear from FIGS. 1A and 1C, even when the amount of ink discharged to the front side of the printing medium (printing duty) is the same, the frequency of occurrence of cockling may differ and the likelihood of ink landing position deviation in back-side printing may also differ.
As described above, when the effect of cockling is determined based on the drawing area of an image to be printed or the total of the amounts of ink discharged to a printing medium, the occurrence of partial cockling may be unable to be accurately determined. Thus, for example, when the technique described in Japanese Patent Laid-Open No. 2007-152787 is used, an unnecessarily increased number of scans may decrease the throughput or an insufficient number of scans in printing for a divided section where partial cockling is likely to occurs and that needs an increased number of scans may lead to a decreased image quality.